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(#) Slices

!!! WARNING: Slices
   This is a warning.

Id
:   `Slices`
Summary
:   Slices
Severity
:   Warning
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   3.2.0 (September 2018)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/SliceDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/SliceDetectorTest.kt)

This check analyzes usages of the Slices API and offers suggestions
based on best practices.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/SliceTest.java:33:Warning: A slice should have at least one
row added to it [Slices]
    Slice slice = new ListBuilder(context, uri, ttl).build();
                  ----------------------------------
src/test/pkg/SliceTest.java:39:Warning: A slice should have at least one
row added to it [Slices]
    ListBuilder lb2 = new ListBuilder(context, uri, ttl); // missing on this one
                      ----------------------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/test/pkg/SliceTest.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.app.PendingIntent;
import android.app.slice.Slice;
import android.content.Context;
import android.net.Uri;
import androidx.slice.builders.GridRowBuilder;
import androidx.slice.builders.GridRowBuilder.CellBuilder;
import androidx.slice.builders.ListBuilder;
import androidx.slice.builders.ListBuilder.HeaderBuilder;
import androidx.slice.builders.ListBuilder.RowBuilder;
import androidx.slice.builders.SliceAction;
import androidx.core.graphics.drawable.IconCompat;

@SuppressWarnings({"unused", "ClassNameDiffersFromFileName", "MethodMayBeStatic"})
public class SliceTest {
    // ListBuilder should have at least one row
    //
    // // This is bad because this results in empty slice
    // Slice slice = new ListBuilder(context, uri, ttl).build()
    //
    // Message:
    // A slice should have at least one row added to it.
    //
    // Explanation:
    // A slice should have at least one row added to it. If the content for
    // the slice is unavailable or being loaded and will update eventually,
    // you should still add all the rows that would represent your slice and
    // indicate that content is being loaded on them, this allows the Slice
    // to be presented correctly and update fluidly.
    public void testMultipleRows(Context context, Uri uri, long ttl) {
        // This is bad because this results in empty slice
        Slice slice = new ListBuilder(context, uri, ttl).build();
    }

    public void testMultipleRows(Context context, Uri uri, long ttl,
            SliceAction primary) {
        ListBuilder lb1 = new ListBuilder(context, uri, ttl);
        ListBuilder lb2 = new ListBuilder(context, uri, ttl); // missing on this one
        RowBuilder rb = new RowBuilder(lb1);
        rb.setPrimaryAction(primary);
        rb.setTitle(null, true /* isLoading */);
    }

    public void testMultipleRowsOk1(Context context, Uri uri, long ttl,
            SliceAction primary) {
        ListBuilder lb = new ListBuilder(context, uri, ttl);
        RowBuilder rb = new RowBuilder(lb);
        rb.setPrimaryAction(primary);
        rb.setTitle(null, true /* isLoading */);
    }

    @SuppressWarnings("UnnecessaryLocalVariable")
    public void testMultipleRowsOk2(Context context, Uri uri, long ttl,
            SliceAction primary) {
        ListBuilder lb = new ListBuilder(context, uri, ttl);
        ListBuilder lb2 = lb;
        RowBuilder rb = new RowBuilder(lb2);
        rb.setPrimaryAction(primary);
        rb.setTitle(null, true /* isLoading */);
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/SliceDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `SliceDetector.testAtLeastOneRow`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("Slices")
  fun method() {
     ListBuilder(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("Slices")
  void method() {
     new ListBuilder(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection Slices
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="Slices" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'Slices'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore Slices ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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